Spatial light modulator and projector

ABSTRACT

A spatial light modulator includes a prism group and satisfies either of the following conditions
 
 d &lt;0.95×λ/(2×( n −1)),
 
 d &gt;1.05×λ/(2×( n −1))
where d is a distance between a reference surface and a flat surface, λ is a wavelength of an incident light, and n is a refractive index of the prism group.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a spatial light modulator and aprojector, and more particularly, to a liquid-crystal spatial lightmodulator.

2) Description of the Related Art

A dot-matrix display device is widely used as an image display device,such as a liquid crystal panel (a liquid crystal display device), acathode ray tube (CRT) display device, and a plasma display device. Thedot-matrix display device displays an image by a number of pixels thatare arranged periodically in two dimensional arrays. However, theperiodic arrangement of the pixels causes a sampling noise thatdeteriorates quality of the image, which makes the image rough and lesssmooth. One of the methods to reduce deterioration of the quality of theimage is disclosed in, for example, Japanese Patent ApplicationLaid-Open No. H8-122709.

The dot-matrix image display device has a light-shielding portion calleda black matrix. The black matrix is an area between each of the pixelsto suppress an unnecessary light. In recent years, it is getting morepopular to watch a large screen from comparatively close distance. Forthis reason, a watcher may recognize a black matrix image in aconventional dot-matrix image display device, resulting in thedeterioration of the quality of the image. The conventional technologydisclosed in the Japanese. Patent Application Laid-Open No. H8-122709can hardly reduce the deterioration of the quality of the image causedby the black matrix image.

One of the ideas to prevent the black matrix image from appearing is toinput a light from the image display device into a prism group. Flatsurfaces of the prism group transmit the light as it is; whilerefracting surfaces refracts the light. The light transmitted the prismgroup includes a straight light from the flat surfaces and a refractedlight from the refracting surfaces. The refracted light is deflected andforms a pixel image on the black matrix area. As a result, the blackmatrix image becomes hard to recognize.

However, the characteristics of each prism element that composes theprism group sometimes cause a diffraction due to a variety of factorssuch as periodic arrangement, depth, arrangement pattern, arrangementpitch. A diffracted light from the prism group is dispersed andirradiated to undesired directions. The diffracted light makes the imageblurred, resulting in the deterioration of the quality of the image.Furthermore, when the diffraction occurs in one region of the imagedisplay device and does not occur in other region, the displayed imagebecomes an image having an uneven light intensity in a lattice-pattern,a further deterioration of the quality of the image.

The present invention is made to solve the above problems. The object ofthe present invention is to provide a spatial light modulator and aprojector that display a smooth image of a high-quality without havingan image of the light shield portion such as the black matrix.

SUMMARY OF THE INVENTION

The spatial light modulator according to one aspect of the presentinvention includes a modulating unit that modulates a light based on animage signal and outputs a modulated light, a refracting part thatrefracts the modulated light, and a flat part that transmits themodulated light. The modulating unit includes a plurality of pixels thatare arranged in a matrix, and a light-shielding portion between each ofthe pixels. The refracting part is a prism group that is composed of aplurality of prism elements, each of the prism elements having at leasta refracting surface. The modulated light from one of the pixels isincident on at least a portion of the prism group. The refractingsurface is oriented to project an image of the pixel over an image ofthe light-shielding portion on a screen at a predetermined distance,making an apex with an angle with respect to a reference surface that isorthogonal to an optical axis at the apex. A distance d between thereference surface and the flat part satisfies either of the followingconditionsd<0.95×λ/(2×(n−1))  (1)d>1.05×λ/(2×(n−1))  (2)where λ is a wavelength of the light, and n is a refractive index of theprism elements.

After passing through the pixel part, the light enters into the prismgroup and is refracted on the refracting surface. The direction of therefraction and the angle of the refraction respectively depend on thedirection of the refraction surface and the angle between the refractionsurface and the reference surface. In the technology of this invention,the light refracted is configured to form the images of the pixels, sothat the images of the pixels are superposed on the images of thelight-shielding portions on the screen at predetermined distance fromthe refraction surface. Consequently, the watchers see the smooth andless-rough image without seeing the image of the light-shieldingportion.

In the prism group, the light is refracted on the refracting surface andthe light is diffracted by the depth of the prism element. Thetechnology of the present invention satisfies any one of the conditions(1) and (2)

If the depth d between the reference surface and the refracting surfacesatisfies the following condition (A)d=λ/(2×(n−1))  (A)the diffraction efficiency improves. In the technology of the presentinvention, preferably, the depth d does not cause the diffraction light,or the diffraction light is weak enough to get blurred. To lessen theeffect of the diffraction, the value of the depth d may be various asfar as the depth d satisfies any one of the conditions (1) or (2).Consequently, the diffraction light lessens and watcher sees thehigh-quality and smooth image without seeing the image of the blackmatrix.

Preferably, any one of the following conditions (3) or (4) is satisfiedd<0.9×λ/(2×(n−1))  (3)d>1.1×λ/(2×(n−1))  (4)More preferably, any one of the following conditions (5) or (6) issatisfiedd<0.7×λ/(2×(n−1))  (5)d>1.3×λ/(2×(n−1))  (6)Satisfying any one of the conditions (3) to (6) lessens the diffractionlight more, so that the watcher sees the higher-quality image.

The spatial light modulator according to another aspect of the presentinvention includes a modulating unit that modulates a light based on animage signal and outputs a modulated light, a refracting part thatrefracts the modulated light, and a flat part that transmits themodulated light. The modulating unit includes a plurality of pixels thatare arranged in a matrix, and a light-shielding portion between each ofthe pixels. The refracting part is a prism group that is composed of aplurality of prism elements, each of the prism elements having at leasta refracting surface. The modulated light from one of the pixels isincident on at least a portion of the prism group. The refractingsurface is oriented to project an image of the pixel over an image ofthe light-shielding portion on a screen at a predetermined distance,making an apex with an angle with respect to a reference surface that isorthogonal to an optical axis at the apex. A distance between thereference surface and the flat part and a distance between the referencesurface and a predetermined point on the refracting surface are arrangedin aperiodic.

The prism group causes the diffraction light and one of the causes isthe periodic arrangement of the prism elements. In the technology of thesecond invention, the distance between the reference surface and therefracting surface and the distance between the reference surface andthe flat surface are aperiodic so that the diffraction light ascribableto the periodic arrangement of the prism elements lessens. Consequently,the watcher sees the high-quality and smooth image without seeing theimage of the black matrix.

The spatial light modulator according to still another aspect of thepresent invention includes a modulating unit that modulates a lightbased on an image signal and outputs a modulated light, a refractingpart that refracts the modulated light, and a flat part that transmitsthe modulated light. The modulating unit includes a plurality of pixelsthat are arranged in a matrix, and a light-shielding portion betweeneach of the pixels. The refracting part is a prism group that iscomposed of a plurality of prism elements, each of the prism elementshaving at least a refracting surface. The modulated light from one ofthe pixels is incident on at least a portion of the prism group. Therefracting surface is oriented to project an image of the pixel over animage of the light-shielding portion on a screen at a predetermineddistance, making an apex with an angle with respect to a referencesurface that is orthogonal to an optical axis at the apex. The prismgroup is arranged in a substantially periodic manner, with number of theperiods per a unit area of 15 or less.

One of the causes of that the prism group causes the diffraction lightis the periodic arrangement of the prism elements. In the technology ofthe third invention, when the prism elements are arranged along by thelines that are substantially straight, the number of the substantiallines (periods) per unit area is 15 or less, so that the diffractionlight ascribable to the periodic arrangement of the prism elementslessens. Consequently, the watcher sees the high-quality and smoothimage without seeing the image of the black matrix.

Preferably, the number of the substantial lines (periods) per unit areais 10 to 12. More preferably, the number is 7 to 9. The smaller numberof the lines lessens the diffraction light ascribable to the periodicarrangement of the prism elements more certainly.

According to still another aspect of the present invention, the unitarea is determined based on numerical apertures of an illuminationoptical system that supplies the light to the modulating unit and aprojection optical system on which the modulated light is incident.Therefore, in the minimal unit area, the periodic arrangement of theprism elements may be limited, so that the light is refracted on therefracting surface of the prism group and the diffraction lightascribable to the periodic arrangement of the prism elements lessens.Consequently, the watcher sees the high-quality and smooth image withoutseeing the image of the black matrix.

The projector according to still another aspect of the present inventionincludes a light source that supplies a light, the spatial lightmodulator according to the above aspects, and a projection lens thatprojects the light from the spatial light modulator to display an imageon a screen. Consequently, the watcher sees the high-quality and smoothimage without seeing the image of the black matrix.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed descriptions of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a projector according to a first embodiment ofthe present invention;

FIG. 2 is a perspective view of a liquid crystal panel according to thefirst embodiment;

FIG. 3 is a schematic of a black matrix according to the firstembodiment;

FIG. 4 is a schematic of the black-matrix image according to aconventional image display device;

FIG. 5 is a cross section of the liquid crystal panel according to thefirst embodiment;

FIG. 6A is a schematic for illustrating a refracting in a prism elementaccording to the first embodiment;

FIG. 6B is a top view of the prism element;

FIG. 7A to FIG. 7D are schematics of projection images according to thefirst embodiment;

FIG. 8A to FIG. 8D are cross sections of various prism groups;

FIG. 9 is a cross section of a prism group according to the firstembodiment;

FIG. 10 is a cross section of a prism group according to a secondembodiment of the present invention;

FIG. 11A and FIG. 11B are schematics of a prism group according to athird embodiment of the present invention;

FIG. 12 is a schematic for explaining a unit area according to the thirdembodiment;

FIG. 13A and FIG. 13B are cross sections of various prism groups withdifferent depths;

FIG. 14A to FIG. 14D are schematics of a prism group according to afourth embodiment of the present invention; and

FIG. 15A and FIG. 15B are schematics of a prism group according to afifth embodiment of the present invention.

DETAILED DESCRIPTION

Exemplary embodiments of a spatial light modulator and a projectoraccording to the present invention are explained in detail withreference to the accompanying drawings.

FIG. 1 is a schematic of a projector according to a first embodiment ofthe present invention. A super-high pressure mercury lamp 101 generatesa light that includes a red light, a green light, and a blue light(hereinafter, “R-light”, “G-light”, and “B-light”, respectively). Anintegrator 104 uniforms an illuminance distribution of the light. Apolarization converter 105 changes the light with the uniformilluminance-distribution into a polarized light such as an s-polarizedlight. The s-polarized light enters into a red-light transmittingdichroic mirror 106R. The red-light transmitting dichroic mirror 1 06Rtransmits the R-light, but reflects the G-light and the B-light. Thedichroic mirrors separate the light into the R-light, the G-light, andthe B-light in order.

After the R-light passes through the red-light transmitting dichroicmirror 106R, a reflecting mirror 107 bends the R-light by 90 degrees.Then a first-color spatial light modulator 110R, which is a transparentliquid-crystal display device, modulates the R light based on an imagesignal corresponding to red. The R-light is still s-polarized when theR-light enters into the first-color spatial light modulator 110R,because the dichroic mirrors do not change the polarization direction.

The first-color spatial light modulator 110R includes a λ/2 wave plate123R, a glass plate 124R, a first polarizing plate 121R, a liquidcrystal panel 120R, and a second polarizing plate 122R. The λ/2 waveplate 123R and the first polarizing plate 121R sandwich a glass plate124R, so that the heat does not distort the λ/2 wave plate 123R and thefirst polarizing plate 121 R. The glass plate 124R is transparent anddoes not affect the polarization. The second polarizing plate 122R maybe attached to the emergent surface of the liquid crystal panel 120R orthe incident surface of a cross dichroic prism 112.

The first-color spatial light modulator 110R modulates the R-light asfollows. The λ/2 wave plate 123R changes the s-polarized R light into ap-polarized R light. After passing though the glass plate 124R and thefirst polarizing plate 121R, the p-polarized R-light enters into theliquid crystal panel 120R. The liquid crystal panel 120R modulates thep-polarized R-light based on the image signal corresponding to red andchanges the p-polarized R-light into an s-polarized R-light. Then thesecond polarizing plate 122R outputs the s-polarized R-light to thecross dichroic prism 112.

The red-light transmitting dichroic mirror 106R deflects the G-light andthe B-light by 90 degrees. The blue-light transmitting mirror 106Greflects the G-light, but transmits the B-light. Then a second-colorspatial light modulator 110G, which is a transparent liquid-crystaldisplay device, modulates the G-light based on an image signalcorresponding to green. The second-color spatial light modulator 110Gincludes a liquid crystal panel 120G, a first polarizing plate 121G, anda second polarizing plate 122G.

The G-light is s-polarized when the G-light enters into the second-colorspatial light modulator 110G. After passing though the first polarizingplate 121G, the s-polarized G-light enters into the liquid crystal panel120G. The liquid crystal panel 120G modulates the s-polarized G-lightbased on an image signal corresponding to green and changes thes-polarized G-light into a p-polarized G-light. Then the secondpolarizing plate 122G outputs the p-polarized G-light to the crossdichroic prism 112.

After passing through the blue-light transmitting mirror 106G, theB-light enters into a third-color spatial light modulator 110B via tworelay lenses 108 and two reflecting mirrors 107. The third-color spatiallight modulator 110B, which is a transparent liquid-crystal displaydevice, modulates the B-light based on an image signal corresponding toblue.

The B-light goes via the relay lenses 108 because the optical path ofthe B-light is longer than those of the R-light and the G-light. Therelay lenses 108 are configured to transmit the B-light to thethird-color spatial light modulator 110B as it is. The third-colorspatial light modulator 110B includes a λ/2 wave plate 123B, a glassplate 124B, a first polarizing plate 121B, a liquid crystal panel 120B,and a second polarizing plate 122B. The configuration of the third-colorspatial light modulator 110B is same as that of the first-color spatiallight modulator 110R and the explanation is omitted.

The B-light is s-polarized when the B-light enters into the third-colorspatial light modulator 110B. The λ/2 wave plate 123B changes thes-polarized B-light into a p-polarized B-light. After passing though theglass plate 124B and the first polarizing plate 121B, the p-polarizedB-light enters into the liquid crystal panel 120B. The liquid crystalpanel 120B modulates the s-polarized B-light based on an image signalcorresponding to blue and changes the s-polarized G-light into ap-polarized G-light. Then the second polarizing plate 122B outputs thes-polarized B-light to the cross dichroic prism 112. Thus, the red-lighttransmitting dichroic mirror 106R and the blue-transmitting dichroicmirror 106G separate the light from the super-high pressure mercury lamp101 into the R-light, the G-light, and the B-light.

The dichroic prism 112 includes two dichroic layers 112 a, 112 b thatare crossed each other. The dichroic layer 112 a reflects the B-lightand transmits the R-light and the G-light, while the dichroic layer 112b reflects the R-light and transmits the B-light and the G-light. Inthis manner, the dichroic prism 112 synthesizes the R-light, theG-light, and the B-light that are modulated by the first-color spatiallight modulator, the second-color spatial light modulator, and thethird-color spatial light modulator, respectively. Then a projectionlens 114 projects the light combined by the dichroic prism 112 onto ascreen 166 to display a full-color image.

The cross dichroic prism 112 synthesizes the R-light, G-light, andB-light effectively. To synthesize the lights effectively, eachspatial-light modulator is configured to output the light with thedifferent polarization direction. When each light enters into the crossdichroic prism 112, the R-light and the B-light is s-polarized while theG-light is p-polarized. This configuration comes from the reflectioncharacteristic of the dichroic layers 112 a and 112 b. The dichroiclayers 112 a and 112 b usually have the better reflection characteristicin an s-polarized light, so that the dichroic layers 112 a and 112 b areconfigured to reflect the R-light and the B-light that are s-polarizedand transmit the G-light that is p-polarized.

FIG. 2 is a perspective view of a liquid crystal panel according to thefirst embodiment. The liquid crystal panel is explained in details withthe liquid crystal panel 120R. The other two liquid display panels 120G,120B have the same configuration except the wave-length region.

The liquid crystal panel 120R includes six layers. The incident R-lightgoes toward a screen 116 passing the layers from the bottom side to theupper side. The layers are in the bottom-up order: an incident-sidedust-proof transparent plate 201; an opposed substrate 202; a blackmatrix layer 203; a liquid crystal layer 204; a TFT substrate 205; andan exit-side dust-proof transparent plate 206. The opposed substrate 202is formed on the incident-side dust-proof transparent plate 201 whilethe TFT substrate 205 is formed on the exit-side dust-proof transparentplate 206. The opposed substrate 202 includes transparent electrodes andso on, and the TFT substrate 205 includes thin film transistors (TFT),transparent electrodes, and so on. The opposed substrate 202 and the TFTsubstrate 205 sandwich the black matrix layer 203 and the liquid crystallayer 204. The black matrix layer 203 is formed on the incident side ofthe liquid crystal layer 204 and used to decrease the leakage of thelight to the outside. The liquid crystal layer 204 is used to display animage.

A prism group 210 is composed of a plurality of prism elements 211 andformed on the exit-side surface of the exit-side dust-proof transparentplate 206, however, may be formed on the second polarizing plate, 122Ror on the incident-side surface of the cross dichroic prism 112.Similarly, the first polarizing plate and the second polarizing platemay be inserted between other layers, such as between the incident-sidedust-proof transparent plate 201 and the opposed substrate 202, betweenthe exit-side dust-proof transparent plate 206 and the TFT substrate205, and so on as an alternative to the structure shown in FIG. 1.

FIG. 3 is a schematic of the black matrix layer 203 that includes ablack matrix part 220 and an opening part 230. The black matrix part 220blocks out the incident R-light so that the incident R-light does not gotoward the screen 116. The black matrix part 220 has predeterminedwidths W1, W2 and is formed with an orthogonal lattice-pattern. Theopening part 230 is a rectangular area that is surrounded by the blackmatrix parts 220 and transmits the incident R-light. After passingthrough the opposed substrate 202 to the TFT substrate 205 while beingmodulated by the liquid crystal layer 204, the incident R-light formsthe image of the pixel (hereinafter, “pixel image”). The position andthe size of the pixel image are corresponding to those of the openingpart 230. CL is a center line of the black matrix part 220, and thecenter lines surrounds an area 240 that appears periodically, which isshown within a heavy-line frame.

FIG. 4 is a schematic of an image projected on the screen 116 by aconventional projector. A zonal black-matrix image 220P surrounds anopening image 230P. An image 240P that appears periodically, which isshown within a heavy-line frame, is corresponding to the area 240. Anintersection point CP is an intersection point of central-line imagesCLPs. All the following embodiments are explained with the images thatthe projection lens 114 projects on the screen 116, because the imagesthat are projected on the screen 116 using the projection lens 114 areconsidered to be essentially same as the images that are projected on avirtual screen without using the projection lens 114, except amagnification. The virtual screen is assumed to be laid at apredetermined distance from the prism group 210. The former image isprojected by the projector 100 and the latter image is projected by thefirst-color spatial light modulator 11OR and the like.

FIG. 5 is a cross section of the liquid crystal panel according to thefirst embodiment. To give a clear explanation, the other components arenot shown. After passing through the opening part 230, the R-lightdiverges conically and enters into the prism group 210 partially. Theprism group 210 includes a refracting surface 212 and a flat surface213. The flat surface 213 is substantially parallel with a surface 230awhere the opening parts 230 are formed. A plurality of prism elements211 are arranged periodically and compose the prism group 210.

FIG. 6A is a schematic for illustrating a refracting in a prism elementaccording to the first embodiment. The refractive index of the mediabetween the prism group 210 and the screen 116 (such as the air) is n1,the refractive index of the material of the prism group 210 is n2, andthe angle between the refracting surface 212 and a reference surface 213a, which is called the angle of gradient, is θ. The reference surface213 a corresponds to the flat surface 213 expanded.

The parallel light of the incident light to the prism group 210 is usedto give a clear explanation. Some lights enter into the flat surface 213and some lights enter into the refracting surface 212. The light thatenters into the flat surface 213 orthogonally goes as it is and projectsthe image on the screen without being refracted. On the other hand, thelight that enters into the refracting surface 212 is refracted whilesatisfying with the following conditional equationn 1·sin β=n 2·sin αwhere α is the angle of the incidence and β is the exit angle that arebased on the normal N of the refracting surface 212.

When the screen 116 is laid at a distance L from the prism group 210,and the light is refracted and moves a distance S on the screen 116, thedistance S satisfies the following equation:S=L×tan(Δβ)Δβ=β−α.The distance S is the moving distance of the opening image 240P on thescreen 116 and configured by the angle θ of the gradient of therefracting surface 212.

Moreover, the direction where the light beam LL2 is refracted depends onthe direction of the refracting surface 212. In other words, thedirection where the opening image is formed on the screen 116 isconfigured by the direction of the refracting surface 212.

The images that are projected on the screen 116 by the R-light areexplained with reference to FIGS. 7(a) to 7(d). FIG. 7A shows an image240P of an area that appears periodically on the screen 116. The lightthat enter into the flat surface 213 substantially orthogonally goesstraight without being refracted and forms the opening image 230P (adirect transmitted image) in the center of the image 240P.

The relationship between the refracting surface and the direction of therefraction is explained with reference to FIG. 6B and FIG. 7. FIG. 6B isa top view of the prism element 211. When the light enters into arefracting surface 212 a, the light is refracted with the direction ofthe refraction, the angle of the refraction, and the quantity of therefraction that are respectively corresponding to the direction of therefracting surface 212 a, the angle θ of the graduation, and the areaP1. The angle between a side 211 a and the central line CL on the blackmatrix layer is formed to be 45 degrees, so that the opening image230Pa, shown in FIG. 7A, is formed to the direction of an arrow and atthe distance S from the opening image 230P (a direct transmitted image).To give a clear explanation, the following two things are assumed in allthe explanations: 1) the projection lens 114 does not bring about a flipvertical and a flip horizontal, 2) the watcher always sees the projector100 from the opposite direction that the light is traveling to. Forexample, the watcher sees an image projected on the screen 116 from thebackside of the screen 116 to see the super-high pressure mercury lamp101.

FIG. 7A to FIG. 7D show the identical image 240P and each opening image:230Pa; 230Pb; 230Pc; and 230Pd. The same explanation as the refractingsurface 212 a and the opening image 230Pa is applied to: the refractingsurface 212 b and the opening image 230Pb that are shown in FIG. 7B; therefracting surface 212 c and the opening image 230Pc that are shown inFIG. 7C; and the refracting surface 212 d and the opening image 230Pdthat are shown in FIG. 7D.

FIG. 8A to FIG. 8D are cross sections of various prism groups. Thedirection of the refracting surface, the angle of the graduation, andthe area determine the shape. FIG. 8A is a sectional view of a prismgroup 810 with a trapezoidal form that includes a refracting surface 810a and a flat surface 810 b. FIG. 8B is a sectional view of a prism group820 with a triangular form that includes a refracting surface 820 a anda flat surface 820 b. FIG. 8C is a sectional view of a prism group 830with a triangular form that includes a refracting surface 830 a and aflat surface 830 b. FIG. 8D is a sectional view of a prism group 840with a blaze form that includes a refracting surface 840 a.

In this manner, the black-matrix image 220 gets blurred 220 using thelight refracted on refracting surfaces 212 a, 212 b, 212 c, and 212 d.Next, the way to decrease the diffraction light is explained Withreference to FIG. 9. To give a clear explanation, the shape of the prismelement shown in FIG. 8B is used.

Two refracting surfaces 920 a form a V-shaped depression that isperiodic. A reference surface 901 is defined to be substantiallyorthogonal to an optical axis of the incident light and includes an apexof the V-shaped depression. A distance between the reference surface 901and a flat surface 920 b is d. The distance d corresponds to the depthof the V-shaped depression and may be called the depth d. The distance dsatisfies any one of the following conditionsd>1.05×λ/(2×(n−1))  (2)where n is the refractive index of the material of a prism group 920 andλ is the wavelength of the incident light to the prism group 920. In thepresent embodiment, the distance d is 1100 nm and, if the depth dsatisfies the following condition (A)d=λ/(2×(n−1))  (A)the diffraction efficiency improves.

In the present embodiment, the incident light is the visible light ofthe light that the super-high pressure mercury lamp 101 generates. Forexample, when the wavelength λ of the incident light is 480 nm and therefractive index n of the prism group 920 is 1.46, the condition (A) is$\begin{matrix}{d = {480/\left( {2 \times \left( {1.46 - 1} \right)} \right)}} \\{= {522\quad{{nm}.}}}\end{matrix}$

Another example is that when the wavelength λ of the incident light is650 nm and the refractive index n of the prism group 920 is 1.46, thecondition (A) is $\begin{matrix}{d = {650/\left( {2 \times \left( {1.46 - 1} \right)} \right)}} \\{= {707\quad{{nm}.}}}\end{matrix}$

The diffraction occurs effectively if the wavelength λ of the incidentlight is 522 nm in the former case and if the wavelength λ of theincident light is 707 nm in the latter case. In the present embodiment,preferably, the depth d of the V-shaped depression does not cause thediffraction light, or lessens the diffraction to get blurred.

In the present embodiment, the value of the distance d may be various asfar as the distance d satisfies any one of the conditions (1) or (2).For example, when the wavelength λ is 480 nm, the conditions (1) and (2)become $\begin{matrix}{{d < {0.95 \times {\lambda/\left( {2 \times \left( {n - 1} \right)} \right)}}} = {0.95 \times {480/\left( {2 \times \left( {1.46 - 1} \right)} \right)}}} \\{{= {496\quad{nm}}},{and}} \\{{d > {1.05 \times {\lambda/\left( {2 \times \left( {n - 1} \right)} \right)}}} = {1.05 \times {480/\left( {2 \times \left( {1.46 - 1} \right)} \right)}}} \\{{{= {548\quad{nm}}},{{respectively}.}}\quad}\end{matrix}$

Another example is that when the wavelength λ is 650 nm, the conditions(1) and (2) become $\begin{matrix}{{d < {0.95 \times {\lambda/\left( {2 \times \left( {n - 1} \right)} \right)}}} = {0.95 \times {650/\left( {2 \times \left( {1.46 - 1} \right)} \right)}}} \\{{= {671\quad{nm}}},{and}} \\{{d > {1.05 \times {\lambda/\left( {2 \times \left( {n - 1} \right)} \right)}}} = {1.05 \times {650/\left( {2 \times \left( {1.46 - 1} \right)} \right)}}} \\{{= {742\quad{nm}}},{{respectively}.}}\end{matrix}$

In the present embodiment, the depth d is 1100 nm and this lengthsatisfies the condition (2) with any wavelengths of the incident light,so that the diffraction light lessens. Accordingly, the watcher sees thehigh-quality and smooth image without seeing the image of the blackmatrix.

In the present embodiment, it is preferable that the following condition(3) or (4) is satisfiedd<0.9×λ/(2×(n−1))  (3)d>1.1×λ/(2×(n−1))  (4)

It is more preferable that the following condition (5) or (6) issatisfiedd<0.7×λ/(2×(n−1))  (5)d>1.3×λ/(2×(n−1))  (6)Satisfying any one of the conditions (3) to (6) lessens the diffractionlight more, so that the watcher sees the higher-quality and smootherimage.

FIG. 10 is a cross section of a prism group 1020 of a spatial lightmodulator according to a second embodiment of the present invention.Except the prism group 1020, the configuration of the second embodimentis basically same as that of the first embodiment and the explanationsof the other components are omitted. In the present embodiment, areference surface 1001 is defined to correspond to a flat surface of asubstrate that includes the prism group 1020, and to be substantiallyorthogonal to an optical axis of the incident light. The distancesbetween the reference surface 1001 and a flat surface 1020 b are d1, d3,d5. The distances between the reference surface 1001 and predeterminedpoints are d2, d4, d6. The predetermined points are the nearest pointsto the reference surface 1001 on the refracting surface 1020 a. Thedistances d1, d3, d5 and the distances d2, d4, d6 are formed to beaperiodic.

One of the causes of that the prism group 1020 causes the diffractionlight is the periodic arrangement of the prism elements. In the presentembodiment, the arrangement of the prism elements is aperiodic, so thatthe diffraction light lessens. Consequently, the watcher sees thehigh-quality and smooth image without seeing the image of the blackmatrix.

FIG. 11A is a perspective view of a liquid crystal panel 1100R of aspatial light modulator according to a third embodiment of the presentinvention. The configuration of the third embodiment is basically sameas that of the first embodiment, therefore, the same reference symbolsas the first embodiment are applied. The liquid crystal panel 1100R isan example of three liquid crystal panels that three special lightmodulators have respectively.

In the present embodiment, a prism group 1110 is composed of a pluralityof prism elements 1111 and the prism elements 1111 are arranged along bylines La1, La2, La3, La4, and La5 that are substantially straight. Thenumber of the lines La1, La2, La3, La4, and La5 per unit area aφ isfive. The number of the lines La1, La2, La3, La4, and La5 per unit areaaφ may be 15 or less.

FIG. 11B is a front view of the neighborhood of the unit area aφ. Theprism elements 1111 are formed with substantially orthogonallattice-pattern. The lines Lb1, Lb2, Lb3, Lb4, Lb5, and Lb6 that aresubstantially straight are substantially orthogonal to the lines La1 toLa5. The unit area aφ may have 15 or less lines that are orthogonal tothe lines La1 to La5.

FIG. 12 is a schematic for explaining the unit area aφ with an opticalpath from the super-high pressure mercury lamp 101 to the screen 116.For convenience, only the main components are shown, the projection lens114 is illustrated to be a single biconvex lens, and the prism group1110 is illustrated separately though the prism group 1110 is includedin the liquid crystal panel 11OOR actually. The projector 100 includesthe components that belong to optical systems such as the illuminationoptical system (hereinafter, “illumination system ILL”), the projectionoptical system (hereinafter, “projection system PL”), and thecolor-separation optical system. The super-high pressure mercury lamp101 and the integrator belong to the illumination system ILL. Theprojection lens 114 belongs to the projection system PL and correspondsto the projection system PL in FIG. 12. Any components that belong tothe color-separation optical system, such as the red-light transmittingdichroic mirror 106, are not shown in FIG. 12.

The optical path from the super-high pressure mercury lamp 101 to thescreen 116 is as follows. The super-high pressure mercury lamp 101outputs the light to the integrator 104. The integrator 104 illuminatesthe liquid crystal panel 1100R with the superposed lights that have apredetermined angle distribution, that is, the superposed lights withthe various incident angles illuminate a position OBJ that is on theliquid crystal panel. The liquid crystal panel 110R outputs the light tothe prism group 1110 while the light spreads with the F-number of theillumination system ILL. The projection lens 114 receives the light thatpasses through the prism group 1110 and projects the light on the screen116 with the F-number that is same as or smaller than the F-number ofthe projection lens 114. The image of the position OBJ is formed on theposition IMG that is on the screen 116 because a position IMG isconjugated with the position OBJ. The F-number of the illuminationsystem ILL (hereinafter, “F-number of ILL”) and that of the projectionsystem PL (hereinafter, “F-number of PL”) satisfy any one of thefollowing three relational expressions (B) to (D)the F-number of ILL>the F-number of PL  (B)the F-number of ILL=the F-number of PL  (C)the F-number of ILL<the F-number of PL  (D)

In any one of the relationships, the smaller F-number of ILL or F-numberof PL determines the angular range, and the light within the angularrange is projected on the screen 116 validly. For example, any one ofthe relational expressions (B) or (C) satisfies the following condition1/(2FILL)=sin θawhere FILL is the F-number of PL, θa is the angle between the opticalaxis and the emergent light of the position OBJ.

The emergent light from the liquid crystal panel 1100R spreads with theangle θa and illuminates the unit area aφ, which is a circular area onthe prism group 1110. Then, the projection lens 114 projects all theemergent light from the unit area on the screen 116. On the other hand,in the relational expression (D), the F-number of ILL determines theunit area aφ that is projected on the screen 116 validly.

In any relational expressions (B), (C), and (D), the projection lens 114projects the emergent light from the unit area aφ on the screen 116. Inthe present embodiment, the prism group 1110 has the prism elements thatare arranged along by the lines La1 to La5 and the lines Lb1 to Lb6 perthe unit area aφ, and the number of the lines La1 to La5 and that of thelines Lb1 to Lb6 are not more than 15, so that the diffraction lightascribable to the periodic arrangement of the prism elements lessens.Consequently, the watcher sees the high-quality and smooth image withoutseeing the image of the black matrix.

In the unit areas aφ, the total area of the refracting surface 212 of aunit areas aφ is equal to those of any other unit areas aφ, and thetotal area of the flat surface of a unit areas aφ is equal to those ofany other unit areas aφ. Therefore, the projection image has lessdiffraction light and the pixel images are superposed on theblack-matrix images on the screen 116 at a predetermined distance fromthe prism group 1110. Consequently, the watcher sees the smooth andless-rough images without seeing the image of the black matrix.

Preferably, the number of the lines that are substantially straight perthe unit area is 10 to 12. More preferably, the number is 7 to 9. Thesmaller number of the lines lessens the diffraction light ascribable tothe periodic arrangement of the prism elements more certainly.

FIG. 13A is a cross section of the prism group 1320 that is made ofglass. The depth d1 is approximately 30 nm and the angle θ1 between thereference surface 1001 and the refracting surface is approximately 0.06degree. FIG. 13B is a cross section of the prism group 1320 made ofacrylic or ZEONEX (a trade name). On the prism group 1320, a resinsubstrate 1330, which is optical transparent, and a glass substrate 1340are formed. The depth d2 is approximately 1 μm and the angle θ2 isapproximately 0.97 degree. The structure shown in FIG. 13B is made moreeasily than that shown in FIG. 13A because the former structure has thelarger values of the depth and the angle than the latter structure.

FIG. 14A to FIG. 14D are schematics of a prism group 1410 of a spatiallight modulator according to a fourth embodiment of the presentinvention. Except the prism group 1410, the configuration of the fourthembodiment is same as that of the first embodiment and the explanationsof the other components are omitted. The prism group 1410 is composed ofthree types of prism elements 1411 a, 1411 b, and 1411 c. When a set ofis considered to have the prism elements 1411 a, 1411 b, 1411 c and 1411b that are arranged in the described order and adhered to each other, aplurality of the sets are adhered to each other to compose the prismgroup 1410. The prism elements 1411 a is a zonal prism element with therefracting surfaces 1412 a, and the prism element 1411 c with therefracting surface 1412 c corresponds the prism element 1411 a that isflipped horizontally. The prism element 1411 b is a parallel flat platethat includes a flat surface 1412 b. The two prism groups 1410 may beoverlapped substantially orthogonally to have the same function as theprism group that includes the flat surface 1411 b and the refractingsurfaces 1411 a, 1411 c that refract the lights that are substantiallyorthogonal each other.

In the present embodiment, the diffraction lessens in the followingsimple way: manufacturing the prism elements 1411 a, 1411 b, and 1411 cthat are substantially flat plates; and arranging 15 or less prismelements 1411 a, 1411 b, and 1411 c per unit area aφ.

FIG. 15A is a front view of a prism group 1510 of a spatial lightmodulator according to a fifth embodiment of the present invention.Except the prism group 1510, the configuration of the fifth embodimentis same as that of the first embodiment and the explanations of theother components are omitted. Prism elements 1511 a, 1511 b, and 1511 cis formed to have the random depths and are arranged in the unit area aφat random. In the unit areas aφ, the total area of the refractingsurface 212 of a unit areas aφ is equal to those of any other unit areasaφ, and the total area of the flat surface 213 of a unit areas aφ isequal to those of any other unit areas aφ.

A manufacturing method of the prism group 1510 is explained withreference to FIG. 15B. To form the prism elements that compose the prismgroup 1510, a piezo actuator (not shown) or the like is used to press asubstrate 1520 that is made of acrylic using a mold 1530 that has apyramid-shaped tip. In the present method, the depth and the directionof the prism element respectively depend on the force and the directionwith which the mold 1530 is pressed into the substrate 1520. When theprism group 1510 is formed according to the present manufacturingmethod, the projection image has less diffraction light, and the pixelimages are superposed on the black-matrix images on the screen at apredetermined distance from the prism group 1510. Consequently, thewatcher sees the smooth and less-rough images without seeing theblack-matrix image.

The present invention does not limit the configurations to fiveembodiments described above. As far as the prism group does not causethe diffraction light, or the prism group lessens the diffraction lightenough so that the diffraction light get blurred, any configurations maybe any combinations of five embodiments.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1. A spatial light modulator comprising: a modulating unit thatmodulates a light based on an image signal and outputs a modulatedlight; a refracting part that refracts the modulated light; and a flatpart that transmits the modulated light, wherein the modulating unitincludes a plurality of pixels that are arranged in a matrix; and alight-shielding portion between each of the pixels, the refracting partis a prism group that is composed of a plurality of prism elements, eachof the prism elements having at least a refracting surface, themodulated light from one of the pixels is incident on at least a portionof the prism group, the refracting surface is oriented to project animage of the pixel over an image of the light-shielding portion on ascreen at a predetermined distance, making an apex with an angle withrespect to a reference surface that is orthogonal to an optical axis atthe apex, and a distance d between the reference surface and the flatpart satisfies either of the following conditionsd<0.95×λ/(2×(n−1))d>1.05×λ/(2×(n−1)) where λ is a wavelength of the light, and n is arefractive index of the prism elements.
 2. A spatial light modulatorcomprising: a modulating unit that modulates a light based on an imagesignal and outputs a modulated light; a refracting part that refractsthe modulated light; and a flat part that transmits the modulated light,wherein the modulating unit includes a plurality of pixels that arearranged in a matrix; and a light-shielding portion between each of thepixels, the refracting part is a prism group that is composed of aplurality of prism elements, each of the prism elements having at leasta refracting surface, the modulated light from one of the pixels isincident on at least a portion of the prism group, the refractingsurface is oriented to project an image of the pixel over an image ofthe light-shielding portion on a screen at a predetermined distance,making an apex with an angle with respect to a reference surface that isorthogonal to an optical axis at the apex, and a distance between thereference surface and the flat part and a distance between the referencesurface and a predetermined point on the refracting surface are arrangedin aperiodic.
 3. A spatial light modulator comprising: a modulating unitthat modulates a light based on an image signal and outputs a modulatedlight; a refracting part that refracts the modulated light; and a flatpart that transmits the modulated light, wherein the modulating unitincludes a plurality of pixels that are arranged in a matrix; and alight-shielding portion between each of the pixels, the refracting partis a prism group that is composed of a plurality of prism elements, eachof the prism elements having at least a refracting surface, themodulated light from one of the pixels is incident on at least a portionof the prism group, the refracting surface is oriented to project animage of the pixel over an image of the light-shielding portion on ascreen at a predetermined distance, making an apex with an angle withrespect to a reference surface that is orthogonal to an optical axis atthe apex, and the prism group is arranged in a substantially periodicmanner, with number of the periods per a unit area of 15 or less.
 4. Thespatial light modulator according to claim 3, wherein the unit area isdetermined based on numerical apertures of an illumination opticalsystem that supplies the light to the modulating unit and a projectionoptical system on which the modulated light is incident.
 5. A projectorcomprising: a light source that supplies a light; a spatial lightmodulator that includes a modulating unit that modulates the light basedon an image signal and outputs a modulated light; a refracting part thatrefracts the modulated light; and a flat part that transmits themodulated light, wherein the modulating unit includes a plurality ofpixels that are arranged in a matrix; and a light-shielding portionbetween each of the pixels, the refracting part is a prism group that iscomposed of a plurality of prism elements, each of the prism elementshaving at least a refracting surface, the modulated light from one ofthe pixels is incident on at least a portion of the prism group, therefracting surface is oriented to project an image of the pixel over animage of the light-shielding portion on a screen at a predetermineddistance, making an apex with an angle with respect to a referencesurface that is orthogonal to an optical axis at the apex, and adistance d between the reference surface and the flat part satisfieseither of the following conditionsd<0.95×λ/(2×(n−1))d>1.05×λ/(2×(n−1)) where λ is a wavelength of the light, and n is arefractive index of the prism elements; and a projection lens thatprojects the light from the spatial light modulator to display an imageon a screen.
 6. A projector comprising: a light source that supplies alight; a spatial light modulator that includes a modulating unit thatmodulates the light based on an image signal and outputs a modulatedlight; a refracting part that refracts the modulated light; and a flatpart that transmits the modulated light, wherein the modulating unitincludes a plurality of pixels that are arranged in a matrix; and alight-shielding portion between each of the pixels, the refracting partis a prism group that is composed of a plurality of prism elements, eachof the prism elements having at least a refracting surface, themodulated light from one of the pixels is incident on at least a portionof the prism group, the refracting surface is oriented to project animage of the pixel over an image of the light-shielding portion on ascreen at a predetermined distance, making an apex with an angle withrespect to a reference surface that is orthogonal to an optical axis atthe apex, and a distance between the reference surface and the flat partand a distance between the reference surface and a predetermined pointon the refracting surface are arranged in aperiodic; and a projectionlens that projects the light from the spatial light modulator to displayan image on a screen.
 7. A projector comprising: a light source thatsupplies a light; a spatial light modulator that includes a modulatingunit that modulates the light based on an image signal and outputs amodulated light; a refracting part that refracts the modulated light;and a flat part that transmits the modulated light, wherein themodulating unit includes a plurality of pixels that are arranged in amatrix; and a light-shielding portion between each of the pixels, therefracting part is a prism group that is composed of a plurality ofprism elements, each of the prism elements having at least a refractingsurface, the modulated light from one of the pixels is incident on atleast a portion of the prism group, the refracting surface is orientedto project an image of the pixel over an image of the light-shieldingportion on a screen at a predetermined distance, making an apex with anangle with respect to a reference surface that is orthogonal to anoptical axis at the apex, and the prism group is arranged in asubstantially periodic manner, with number of the periods per a unitarea of 15 or less; and a projection lens that projects the light fromthe spatial light modulator to display an image on a screen.